Addiction is a debilitating, chronically relapsing disorder, characterized by continued use of drugs, despite negative consequences. Addiction is particularly difficult to treat in the clinical setting due to the high probability of relapse evenafter prolonged periods of abstinence. Risk of relapse increases after exposure to drug-related cues or to environmental stimuli previously associated with drug-use. However, the most substantial increase in risk for relapse to drug-seeking behavior occurs with exposure to stress. Previous studies have implicated the bed nucleus of the stria terminalis (BNST) in stress-induced reinstatement of drug-seeking behavior. In particular, norepinephrine signaling through 2-adrenergic receptors (2 -ARs) in the BNST has been shown to modulate stress-induced reinstatement of drug-seeking behavior. 2 -AR agonists locally administered into the BNST attenuate stress-induced reinstatement behavior. Understanding the mechanism by which 2-AR agonists block stress-induced reinstatement may lead to the identification of new pharmacological therapies to be used for the prevention of stress-induced relapse to drug-seeking behavior. Previous work has shown that the 2A -AR agonist, guanfacine, depresses excitatory neuronal transmission in the BNST. However, recent studies have shown that 2 -ARs are capable of differentially modulating specific excitatory inputs to the central nucleus of the amygdala (CeA) which is a brain structure closely related to the BNST. Therefore, we will be testing the hypothesis that 2A-ARs differentially modulate excitatory inputs to the BNST from the insular cortex, the basolateral amygdala, and the parabrachial nucleus using optogenetic techniques. In addition, recent studies have demonstrated a potential role for 2A -ARs in enhancing excitatory transmission in the BNST. Therefore, we will be testing the hypothesis that a population of neurons in the BNST is activated by 2A -ARs, and we will work to explore properties of this neuronal population. We hope to gain a better understanding of how 2A-ARs modulate excitatory inputs to the BNST, and how modulation of these inputs affects neuronal activation in the BNST. Such an understanding may help to elucidate mechanisms by which 2-ARs in the BNST can modulate stress-induced reinstatement of drug-seeking behavior, and may lead to the identification of new pharmacological therapies for preventing stress-induced relapse to drug-seeking. The primary mentor of this project, Dr. Danny Winder, has many years of experience in stress and addiction research, and in electrophysiological techniques in brain slice preparations. I will be trained in electrophysiological techniques in brain slice preparation, and will work under direct supervision of my advisor to establish optogenetic methodologies for the lab. I will also learn experimental skills and techniques through didactic coursework, and through weekly seminars, journal clubs, and lab meetings. The skills gained during my graduate training will be invaluable to my future career goals as a physician-scientist studying the neural mechanisms underlying the interaction of stress and addiction. PUBLIC HEALTH RELEVANCE: Drug addiction is particularly difficult to treat due to high likelihood of relapse into drug-seeking behavior, even after prolonged periods of abstinence from drugs of abuse. Risk of relapse into drug-seeking behavior is particularly high during times of stress, and 2-adrenergic receptors have been shown to regulate stress- induced relapse. The proposed project seeks to determine the neural mechanisms that could contribute to the ability of 2-adrenergic receptors to block stress-induced reinstatement of drug-seeking behavior.